A superconducting cable has at least one electrical conductor composed of a specific material which changes to the superconducting state at sufficiently low temperatures. The electrical resistance of a correspondingly designed conductor thus tends to zero. Suitable materials are, for example, YBCO (yttrium-barium-copper-oxide) or BiSCCO (bismuth-strontium-calcium-copper-oxide) By way of example, sufficiently low temperatures for a material such as this are between 4 K and 110 K, in order to achieve the superconducting state. Suitable coolants are, for example, nitrogen, helium, neon and hydrogen or mixtures of these substances, in each case in a gaseous or liquid state. Superconducting cables with a cold dielectric and with a warm dielectric are known.
In a superconducting cable with a cold dielectric, the superconducting conductor is surrounded by a dielectric which is composed of layers of insulating material and in which the dielectric contains a liquid cooling medium as an impregnation means. A cable such as this comprises, for example, the conductor as an inner conductor and a screen or return conductor, which is arranged concentrically with respect to the inner conductor, which conductors are kept isolated from one another and at a distance from one another by the dielectric (insulation). A corresponding cable is surrounded by a cryostat which carries a coolant and comprises two concentric metallic tubes which are insulated from one another by thermal insulation.
The cable according to EP 1 717 821 A1 as described initially is a superconducting cable with a warm dielectric, in which the superconducting conductor is arranged directly in a cryostat which carries the coolant. The dielectric or the insulation and the screen, which can also be used as a return conductor, are in this case fitted over the cryostat. This known cable is also equipped with a normal conductor, which is composed of normally conductive material, such as copper, and, for example, carries the current in the event of failure of the cooling or in the event of a short circuit. In the event of a short circuit, the energy that is introduced is dissipated via the coolant. In order to achieve a good current distribution in this cable, specific conductor geometries, in particular specific twist angles, are required both for the superconducting conductor and for the normal conductor.